Like the main games, there are occasions in which you will encounter a Pokémon swarm. These act similar to how Pokémon appear when using a password, but run completely independant. At the start of a random turn, you will be informed of a swarm within one of the nations. These swarms will last for the entire in-game month and provide various Pokémon for you. These Pokémon typically cannot be found elsewhere in the game so this can be the only way to find them.